Method and a device for electro microsurgery in a physiological liquid environment

ABSTRACT

A method and device for electrical emulation of pulsed laser is disclosed. The device utilizes high voltage electrical discharges of sub-microsecond duration in a liquid medium to produce cavitation bubbles of sub-millimeter size for use in high speed precision cutting. Such bubbles are produced by a micro-electrode ( 1.6 ) having a central wire having a diameter of 1 microns to 100 microns embedded in an insulator. A coaxial electrode ( 1.9 ) surrounds the insulator, and may be spaced from the outer surface of the insulator to provide a path for removing tissue.

FIELD OF THE INVENTION

The invention is a method and a device that allows for the electricalemulation of the microsurgical abilities of pulsed lasers. These lasersare the basis for new laser procedures that are responsible for highspeed and high precision cutting action in biological liquidenvironments with minimal damage to the surrounding mechanism. They workby producing cavitation bubbles. The action of these lasers and laserprocedures are simulated in the current invention by using protocolsthat are a part of this invention. These protocols regulate theelectrical current injected into the specialized device that has beendevised. As a result it is possible to emulate the cavitation bubbleformation cutting that has become a hallmark of various pulsed laserprocedures. The invention allows the same device to be used for such anemulation of these cavitation bubbles while also allowing for heatinduced coagulation and poration of biological materials.

BACKGROUND OF THE INVENTION

Various pulsed lasers have been applied to soft tissue cutting andremoval in a liquid environment. Three basically different mechanisms oflight absorption have been involved in laser surgery: (1) linearabsorption of light by tissue (I. Turovets, D. Palanker, Y. Kokotov, I.Hemo, A. Lewis, J. Appl. Phys. 79(5): 2689-2693 (1996); D. Palanker, I.Turovets, A. Lewis, Laser-Tissue Interaction VII, Proc. SPIE 2681(1996)); (2) linear absorption of light by the medium (P. D. Brazitikos,D. J. D'Amico, M. T. Bernal, A. W. Walsh, Ophthalmology 102 (2): 278-290(1994); C. P. Lin, D. Stern, C. A. Puliafito, Invest. Ophthalmol. Vis.Sci 31(12): 2546-2550 (1990)); or (3) non-linear absorption by tissue ormedium associated with dielectric breakdown of the material (A. Vogel,S. Busch, K. Jungnickel, R. Birngruber, Lasers Surg. Med. 15: 32-43(1994)). In spite of differences in the mechanisms of laser radiationabsorption in tissue, the mechanism of tissue disruption with pulsedlasers has been generally associated with an explosive expansion ofoverheated liquid and subsequent cavitation bubble formation. As aresult, material disruption occurs in the light absorption zone and in azone of fast expansion and collapse of cavitation bubbles (I. Turovets,D. Palanker, Y. Kokotov, I. Hemo, A. Lewis, J. Appln. Phys. 79(5):2689-2693 (1996); P. D. Brazitijos, D. J. D'Amico, M. T. Bernal, A. W.Walsh, Ophthalmology 102(2): 278-290 (1994); and A. Vogel, S. Busch, K.Jungnickel, R. Birngruber, Lasers Surg. Med. 15: 32-43 (1994)).

In view of the general complicated nature of laser-based devices asearch was made for ways to emulate with non-laser methodologies themechanisms that are known to occur with available lasers. In the case ofcavitation bubble generation it is known, as described above, that thesebubbles result from local and fast heat energy deposition. Thus, it islogical to consider an overheating of a conductive medium with a shortpulse of electric current in order to generate an action which issimilar to such pulsed laser. The invention described herein realizessuch electro microsurgery in a physiological medium with a specificpotential for applications in ophthalmology. Previous investigators whohave considered pulsed electrical techniques and have seen cavitationbubble formation (R. Vorreuther, R. Corleis, T. Klotz, P. Bernards, U.Englemann, J. Urology 153: 849-853 (1995); R. Lemery, T. K. Leung, E.Lavallee, A. Girard, M. Talajic, D. Roy, M. Montpetit, Circulation83(1): 279-293 (1991)) considered these bubbles either as an undesiredside effect or as a means for shock wave generation for hard tissuedestruction. These electrosurgical devices were designed for relativelyhigh energy pulse generation: between 25 mJ and 40 J and with relativelylong pulse duration: hundreds of microseconds. Such high energy pulsesresulting in a few millimeter-sized cavitation bubbles cannot be appliedto microsurgical applications such as those envisioned in delicateorgans such as the eye. To accomplish such delicate cavitation bubblebased microsurgery, a new electrical system based on an asymmetricmicroelectrode that enables generation of hundreds of thousands ofcavitation bubbles, is described. This can become an alternative toendo-laser equipment in such areas as vitreoretinal surgery.

The concept can also be extended to the electroporation of individualcells and assemblies of cells in which the state of the prior art is amacroscopic device with macroscopic electrodes placed in a large bathwith a solution of cells (M. Joersbo and T. Brunstedt, PhysiologiaPlantarium 81: 256-264 (1991)). Instead of this a microelectrode forlocal electroporation of individual cells is used, or alternatively, anarray of microelectrodes could be applied for poration of assemblies ofcells.

In addition, by varying the nature of the characteristics of theelectrical current the same device can be used for cavitation bubblecutting, electroporation or coagulation.

STATE OF PRIOR ART

Electrosurgical devices are widely used in surgery. The majority ofthese techniques are based on heating the tissue by an RF current andthis local heat deposition causes one of the following processes:coagulation, and/or water evaporation. As a result, the only capabilityof such devices is to cut soft tissues by heat deposition which causessignificant coagulation in the area surrounding the cut tissue. Suchdevices are totally useless for endolaser applications, for example inthe eye. In addition to such RF techniques, DC pulsed electricalmethodologies have not achieved a widespread acceptance because theabsence of coagulation was considered an undesirable effect. In thepast, cavitation bubbles were generated by DC pulsed methodologies.However, these techniques, which were designed for relatively highenergy pulse generation (tens of milliJoules) with relatively long pulsedurations (hundreds of microseconds), were only used as a means forshock wave generation for hard tissue destruction (R. Vorreuther, R.Corleis, T. Klotz, P. Bernards, U. Engelmann, J. Urology 153: 849-853(1995)). These high energy pulses resulted in cavitation bubbles withdimensions of a few millimeters, and these have no applicability to, forexample, eye microsurgery in which considerably smaller bubbles arerequired. Laser-based techniques indicate that the pulse energiesrequired to produce such bubbles are in the range of a few tens ofmicroJoules and the pulse durations required are generally in asub-microsecond range (D. Palanker, I. Hemo, I. Turovets, H. Zauberman,A. Lewis, Invest Ophthal. Vis. Sci. 35: 3835-3840 (1994); C. P. Lin, Y.K. Weaver, R. Birngruber, J. P. Fujimoto, C. A. Puliafito, Lasers Surg.Med. 15: 44-53 (1994)). In addition to these differences in thetime/energy characteristics of the available DC pulsed technologies ascompared the present invention, it is required that any device forapplications such as vitreoretinal surgery should be able to withstandtens of thousands of pulses. The previous high energy devices describedabove have a lifetime of less than 100 pulses (R. Vorreuther, R.Corleis, T. Klotz, P. Bernards, U. Engleman, J. Urology 153: 849-853(1995) and this is by far not sufficient for the microsurgicalapplications that are envisioned.

In terms of cell poration, the prior art were again macroscopic deviceswith macroscopic electrodes placed in a large bath (M. Joersbo and J.Brunstedt, Physiologia Plantarium 81: 256-264 (1991)) with a solution ofcells.

SUMMARY OF THE INVENTION

The method and device of the present invention are based on producingsubmicrosecond high voltage discharges in physiological media withspecial protocols designed for the generation of cavitation bubbles forsoft tissue microsurgery in a liquid environment as is possible todaywith certain pulsed lasers. The device consists of a combination ofthree elements:

a specific microelectrode structure,

specific electrical protocols to develop the required pulsecharacteristics to emulate pulsed laser microsurgery with cavitationbubble generation in the same device that can produce other electricalprotocols for tissue coagulation and electroporation; and

the above protocols determine the characteristics of the HV pulsegenerator that is to be used.

DESCRIPTION OF THE INVENTION

The foregoing features of the invention are illustrated in theaccompanying drawings, in which:

FIG. 1A is a schematic illustration of a microelectrode in accordancewith the invention, utilizing a single wire and having a taperedinsulator with a flat tip;

FIG. 1B is a schematic illustration of a microelectrode in accordancewith the invention, utilizing a single wire and having a nontaperedinsulator with a flat tip;

FIG. 1C is a modification of the device of FIG. 1A, wherein theinsulator has a rounded tip;

FIG. 1D is a modification of the device of FIG. 1B, wherein theinsulator has a rounded tip;

FIG. 2 is a schematic diagram of a high voltage generator connected tothe microelectrode of FIGS. 1A-1D;

FIG. 3A is a schematic illustration of a microelectrode in accordancewith the invention, having multiple wires;

FIG. 3B is a schematic illustration of a partially bent, single-wiremicroelectrode in accordance with the invention, having a flat tip;

FIG. 3C is a schematic illustration of a single-wire side-firingmicroelectrode in accordance with the invention, having a flat tip;

FIG. 4A and 4B are schematic top and side views, respectively, of amicroelectrode array;

FIG. 5A is a graphical illustration of the time dependence of electrodepotential (U) and current passing through the exit surface of anelectrode (-I) during a discharge, the electrode having a wire diameterof 25 μm;

FIG. 5B is a graphical illustration of a second discharge, followingthat illustrated in FIG. 5A;

FIG. 6 is a sequence of micrographs illustrating the dynamics ofcavitation bubbles generated at a potential (U_(max)) of 2.7 kV,utilizing an electrode having a wire diameter of 20 μm and a tipdiameter of 200 μm, at a magnification of 100×, the delay between theelectric pulse and the flash pulse being shown in μs in each frame

The Microelectrodes

One way to form the microelectrodes, or needles, of the presentinvention is to seal a thin metal wire (1.5) into an insulator (1.2)with a variety of structures that can be tapered (FIGS. 1A & 1C) or haveother geometries (FIGS. 1B & 1D). The wire (1.5) has a diameter at itsexit from insulator (1.2) in the range of 1-100 microns. This insulator(1.2) and wire (1.5) creates an internal (main) electrode (1.1). Asecond electrode (1.3) is provided to mechanically protect the mainelectrode. This may be formed by coating the surrounding insulator (1.2)with a metallic coating (1.3) (see FIG. 1A). The resulting externalelectrode can play the role of a protective metal cover for the maininner electrode (1.1). The geometry of this microelectrode and itsconnection to the output terminals (2.1) and (2.2) of the HV pulsegenerator (2.3) are schematically shown in FIG. 2.

As shown in FIG. 2, the main electrode is placed in a conducting medium(2.4). The high voltage (HV) generator (2.3) produces electricalsubmicrosecond duration discharges through a gas layer in the conductingliquid-containing environment which produces cavitation bubbles withcharacteristics which emulate the action of pulsed lasers in a liquidmedium. The bubbles are of sub-millimeter sizes. Such cavitation bubblesprovide a mechanism for soft tissue microsurgery in a physiologicalmedium, such as in the eye.

The microelectrode may be fabricated by pulling a glass microcapillarytube having a metal wire inside the tube. The tube is heated and pulledto produce the tapered shape of FIG. 1A, with the glass forming theinsulator (1.2). Alternatively, the microelectrode can be fabricatedusing microlithography. The device may be used as a single device ormultiple microelectrodes may be mounted in an array, as illustrated inFIGS. 4A and 4B, for use in microcutting or microperforation ofmaterials, such as aggregates of cells.

The outer dimensions of the microelectrode (1.4) can be chosen accordingto the requirements of the application. For example, for microsurgicalapplications they could be similar to that of laser tips applied inendolaser microsurgery.

The diameter of the insulator around the exit of the main electrode(1.1) should be large enough to have mechanical strength whilepreventing the puncture of soft tissue. On the other hand, it should besmall enough to enable it to reach the tissue to be cut at variousangles. These requirements determine the range of the diameter ofelectrode (1.1) to be: 0.05-0.4 mm. It is useful to have rounded edgesof the insulator (FIG. 1C, 1.6) in order to keep the electrode wire(1.5) in close proximity to the treated tissue when the tip is held atdifferent angles relative to the tissue surface. The diameter ofinsulator (1.2) inside the second electrode (1.3) should be as large aspossible to decrease the capacitance of the electrodes in the conductiveliquid environment, and could be equal to the inner diameter of theexternal electrode (1.3). In certain cases (1.2) could be smaller than(1.3) in order to provide a gap (1.9) between electrode 1.3 andinsulator (1.2) (FIG. 1A) to allow suction during the treatment. Suchsuction allows lifting of treated tissues and the evacuation of gasbubbles and tissue debris that results from tissue cutting by thegenerated bubbles.

The outer diameter of the second (external) electrode (1.4) should be0.9-1 mm, as this is standard equipment for instruments used in certainmicrosurgical procedures used in vitreoretinal surgery.

The total length (1.7) of the microelectrode (FIG. 1A) is 38-40 mm toallow for access to all the areas inside the eye ball for suchvitreoretinal surgery. Other microsurgical procedures may require otherdimensions.

The same structure could be used with, for example, a set of multiplewires as the inner electrode (see FIG. 3A, 1.8) or the tip can bepartially bent in order to fire the cavitation bubble at an angle (FIG.3B) or can have a geometry that can produce a cavitation bubble at rightangles to the axis of the electrode (FIG. 3C). All the electrodeconfigurations shown in FIGS. 3A-3C can also have electrode andinsulator geometries with the structures that are seen in FIGS. 1A-1D.

Electrical Protocols to Emulate Pulse Laser Induced Cavitation Bubbles

To achieve the high cutting efficiency of the pulsed laser treatmentsthat are currently being developed, cavitation bubbles should be createdfast enough for generation of high pressures and high boundary velocityand acceleration. These requirements determine the minimal peak power ofthe pulse. On the other hand, the cutting action should be local enoughfor prevention of extensive damage in the surroundings of a lesion. Thisrequirement limits the total energy imposed on the bubble formation.Based on the experience of laser-induced cavitation (D. Palanker, I.Hemo, I. Turovets, H. Zauberman, A. Lewis, Invest Ophthal. Vis. Sci 35:3835-3840 (1994); C. P. Lin, Y. K. Weaver, R. Birngruber, J. G.Fujimoto, C. A. Puliafito, Lasers Surg. Med. 15: 44-53 (1994)), thediameter of the cavitation bubble required for precise and effectivecutting of vitreoretinal tissue should be in a range of 0.4-0.5 mm, thatcorresponds to the bubble energies in a range of 3 to 6 μJ.

The High Voltage Pulse Generator

The foregoing protocols determine the characteristics of the highvoltage pulse generator. The electrode diameter 1.5 has to be capable ofgenerating single pulses and pulse trains with a pulse duration varyingin a range of 30 ns-3 μs, and the generator must be capable of varyingthe voltage amplitude in the range of 100 V-10 kV. The peak currentduring the pulse can reach a few Amperes.

In addition to pulse generation aimed at cavitation bubble generationand tissue cutting, electrical pulses with lower voltage and, possibly,longer pulse duration could be applied with the above electrodes forelectroporation of individual cells or for cell layers. Furthermore, theelectrical power supply can also be amended so that this invention canalso have the added capability of a coagulation.

Extension of the Invention to Parallel Devices

Similar electrode geometries and pulse protocols can be envisioned toproduce a parallel array of electrodes for the generation of a parallelarray of cavitation bubbles and/or heating for producingbioelectromechanical field effects on multiple biological cells at onetime (see FIG. 4).

Applications of the Device

Numerous applications of the invented device are possible in the fieldof soft tissue microsurgery based on the cutting action of the generatedcavitation bubbles. One of the most promising for the single electrodeis vitreoretinal membrane removal, because the accepted mechanicalpeeling and cutting of such membranes is often associated with retinaldamage. Furthermore, the present device can be used in all microsurgicalprocedures in physiological media (or other conducting liquids),including microsurgery of the internal organs.

In addition, with the modified electrical characteristics the devicecould also be used for bioelectromechanical effects of individual cellsand cell layers, and coagulation of tissue.

Furthermore, the bent, cantilevered tips that produced in this inventioncan be of considerable value in other areas of science and technology.For example, such cantilevered electrodes can be produced such that thecantilever is very flexible (Force constants of a few N/m) and the tipis very small (0.05 μ). With such an extension of the presentmethodology, together with the pulsed protocols that have beendeveloped, and that have been described herein, controlled alteration ofsurfaces can be effected that will allow fine lithographic patterning ofsuch surfaces.

Experiments

Analysis of the Modes of the Electrical Discharge of the Device

The pulse protocols that have been invented and are described hereinwere developed as a result of detailed experimentation that allowedclose emulation of the effects of pulsed laser cavitation bubblegeneration.

Specific examples of these experiments are described in this section.For example, for an electrode with a wire diameter (1.5) of 25 μm thepulse profiles of the electrode potential (U) and the current passingthrough the exit surface of the electrode (I) are presented in FIG. 5.At U_(max)=0.3 kV (FIG. 5A, curves 1) the voltage and currentsimultaneously decrease with a time constant of about 0.6 μs. As thepotential increases, the nature of the discharge changes: The currentdrops much faster after about 0.2 μs, resulting in slowing down thevoltage reduction (FIG. 5A, curves 2). At U_(max)=0.7 kV (FIG. 5A,curves 3), the current falls to zero (switched off) when the potentialis still at half of the maximum. This switching off of the currentresults from gas generation on the surface of the electrode thatdisconnects the liquid from the metal surface.

As the electric field in the gas layer becomes high enough, an electronavalanche is generated in this layer, that then propagates inside theliquid. This results in the second pulse of current generated after thefirst one (see FIG. 5B), and with increase of the voltage the delaybetween these two pulses decrease. At U_(max) higher than 1.4 kV (FIG.5B, curve 6), these two pulses completely overlap and at U_(max) 2.7 kV(FIG. 5B, curve 7), they became indistinguishable. The discharge at thevoltage range of 1.4-2.7 kV was accompanied by an emission of reddishlight and a sound wave generation. At U_(max)=2.6 kV, the dimensions ofthe lighted spot was about 7 μm. The best emulation of the laser cuttingwas achieved with a range of high voltage that is 2-2.7 kV.

Cavitation Bubble Dynamics

The sequence of micrographs of cavitation generated at the electrodewith a 20 μm wire at U_(max)=2.7 kV is shown in FIG. 6. The delay timebetween the electric pulse and the flash of the dye laser is shown (inμs) in the corner of each frame. The spark generated in the vicinity ofthe electrode is clearly seen as a white spot in front of the wire. Theaverage velocity of the bubble boundary during the first 1 μs of thegrowth phase (frames 1,2) was about 90 m/s. The primary cavitationbubble grew in about 25 μs (frames 2,3) reaching the maximal diameter ofabout 0.5 mm. During the collapse, the bubble had a mushroom-like shape(frame 4) that was eventually transformed to a ring and a stemconnecting its center with the center of the tip (frame 5). Thesecondary bubbles were generated from both the ring and the stem (frames6,7). These bubbles were ejected away from the tip at differentvelocities (about 5 and 17 m/s, respectively) and then collapsed anddisappeared at distances of about 0.25 and 0.65 mm, respectively, atabout 76 μs after the pulse (frame 8).

Tissue Cutting

Post-mortem fresh bovine eyes were prepared as an eyecup preparation:the anterior segments of the eyes and vitreous were removed and theeyecup was filled with Hartmann's physiological solution. Formeasurements of a cutting rate, 4-5 cuts of about 1 cm length wereproduced at the repetition rate of 30 Hz. Cutting efficiency wasdetermined at the speed of the full depth cutting of retina. Cutting ofretina with the rate exceeding 1 mm/s was observed at pulse energies ofabout 80 μJ/pulse with the electrode wire diameter varying in a range10-25 μm. The retinal tissue in the immediate vicinity of the ablatedregion looked normal, and the borders of the lesion were quite sharp andclean.

These experiments are the first step in demonstrating a variety ofdelicate surgical procedures that will evolve as a result of theapplication of this new device and method. For example, themicroelectrode (1.1) can be connected to a catheter (1.10) or othersupport mechanism for manipulation. If desired, the gap 1.9 may serve asa conduit for the delivery of drugs to the regions of the tip of themicroelectrode. Such delivery can be done simultaneously with the bubblecutting of the tissue.

What is claimed is:
 1. A device consisting of: a microelectrode formedof a single metal wire inside an insulator, said insulator having adiameter of less than about 1 mm and said wiring having an exit diameterof less than 100 microns; a second electrode surrounding said insulator;and a high voltage pulse generator capable of producing a voltage in therange of 100 V to 10 kV connected between said wire and said secondelectrode for generating a pulse having a duration in the range of 0.030to 3 μs that causes generation of a submicrosecond duration discharge ina conducting medium between said wire and said second electrode withpulse energies in the range of 1-1000 μJ.
 2. The device of claim 1,wherein said wire has an exit diameter of between 1 and 100 microns. 3.The device of claim 2, wherein said insulator is tapered.
 4. The deviceof claim 3, wherein said insulator is pulled glass.
 5. The device ofclaim 1, wherein said wire has an exit diameter of between 5 and 40micrometers.
 6. The device of claim 1, wherein said second electrode isa coating on said insulator.
 7. The device of claim 1, wherein saidsecond electrode has an outside diameter of less than 1 mm.
 8. Thedevice of claim 1, wherein said discharge has a duration sufficient toproduce a cavitation bubble having a diameter of between 0.4 and 0.5 mm.9. A device consisting of: a microelectrode formed of a single metalwire inside an insulator, said wire having an exit diameter of less than100 microns; an electrode surrounding said metal wire and saidinsulator, said electrode having a diameter between 0.9 and 1.0 mm; anda high voltage pulse generator capable of producing a voltage in therange of 100 V to 10 kV connected to said wire for generating pulseshaving durations of between 30 ns and 3 μs to cause generation ofsubmicrosecond duration sparks in a conductive medium between said wireand said electrode, the generated pulses having pulse energies in therange of 1-1000 μJ.
 10. The device of claim 9 wherein said sparksproduce cavitation bubbles having diameters of between 0.4 and 0.5 mm.11. The device of claim 9, wherein said electrode comprises a conductivecoating on said insulator.
 12. The device of claim 9, further includinga gap between said insulator and said electrode.
 13. The device of claim9, wherein said insulator is pulled glass to produce a tapered insulatorand an exit wire diameter of between 1 and 100 microns, and wherein saidelectrode is a conductive coating on said insulator.
 14. A devicecomprising: a microelectrode comprising a glass microcapillary having ametal wire inside the glass, the microcapillary being tapered to a pointand coated with metal to form a concentric metal needle, said metal wirehaving an exit diameter in the range of 1-100 microns; and a highvoltage pulse generator connected to said wire to generate asubmicrosecond duration discharge in a conducting liquid containingmedium with pulse energies in the range of 1-1000 μJ to produce acavitation bubble, said discharge having a duration sufficiently shortto produce a bubble having a diameter no greater than 0.5 mm in saidconducting medium with characteristics that emulate the action of pulsedlasers in said conducting medium.
 15. A device comprising: amicroelectrode comprising a glass microcapillary having a metal wireinside the glass, the microcapillary being tapered to a point and coatedwith metal to form a concentric metal needle, said metal wire having anexit diameter of less than 100 microns; and a high voltage pulsegenerator connected to said wire to generate an electrical dischargehaving a duration in the range of 0.030 to 3.0 microsecond in aconducting liquid containing medium with pulse energies in the range of1-1000 μJ to produce in said conducting medium submillimeter-sizedcavitation bubbles with characteristics that emulate the action ofpulsed lasers.
 16. A device comprising: a microelectrode comprising aglass microcapillary having a metal wire inside the glass, themicrocapillary being tapered to a point and coated with metal to form aconcentric metal needle, said metal wire having an exit diameter in arange of 1-100 microns; and a high voltage pulse generator connected tosaid metal wire and having a pulse shaped to generate at the metal wireexit a submicrosecond duration electrical discharge through a gas layerin a conducting liquid containing environment with a pulse energy in therange of 1-1000 μJ to produce cavitation bubble generation in saidconducting medium in a manner that produces cavitation bubbles whichcollapse after reaching a maximum diameter of 0.5 mm, withcharacteristics that emulate the action of pulsed lasers in saidconducting medium.
 17. A device as recited in claim 14, 15 or 16,further including a second electrode.
 18. A device as recited in claim14, 15 or 16, further including a second electrode, and a gap betweensaid second electrode and said microelectrode for lifting treated tissueby suction of said medium through this gap, and the evacuation of gasbubbles and tissue debris that result from tissue cutting.
 19. A deviceas in claim 14, 15 or 16, further including means for attachment to acatheter for the simultaneous delivery of drugs to a treated area.
 20. Adevice as in claim 14, 15 or 16, in which said microelectrode iscomposed of multiple metal wires inside said insulator.
 21. A device asin claim 14, 15 or 16, in which said microelectrode includes a tip whichis bent at an angle with the axes of the microelectrode that can varyfrom a few degrees to as much as 180 degrees with respect to themicroelectrode axis.
 22. A device as in claim 14, 15 or 16, in which atip of the microelectrode is bent in a manner that causes a resultingaction at the surface of said medium to occur at an angle with the axisof said microelectrode, and wherein the axis of the microelectrodedefines a cantilever that is flexible enough to bend and measure surfaceforces so that such a device can cause fine alterations on a surfacewith resolutions that can be sub-micrometer to nanometer in dimension.23. A device as in claim 14, 15 or 16, in which the microelectrode has aflat tip or an angled tip.
 24. A device as in claim 14, 15 or 16, inwhich the microelectrode has a round tip.
 25. A device as in claim 14,15 or 16, comprising an array of parallel microelectrodes generating aparallel array of cavitation bubbles.